Moderate severity
Feline Herpesvirus (FHV-1)
The other major cause of "cat flu" alongside calicivirus. This virus targets the eyes and nose, causing sneezing, streaming eyes and — like cold sores in people — flare-ups that recur for life.
⚠️ Common symptoms
Feline herpesvirus is, with calicivirus, one of the two principal agents behind the syndrome owners know as "cat flu". Where calicivirus is notorious for mouth ulcers, herpesvirus is the eye-and-nose specialist: its hallmark is a cat with streaming, sore eyes and relentless sneezing. Also called feline viral rhinotracheitis, it is extremely widespread, and the great majority of cats are exposed to it at some point in their lives.
What makes herpesvirus distinctive is its permanence. Much like the cold-sore virus in humans, FHV-1 never truly leaves the body once it has taken hold. After the first illness it retreats into the nervous system and lies dormant, only to reawaken when the cat is stressed or run down — a house move, a new arrival, a stay in a cattery, or an unrelated illness can all trigger a fresh bout of sneezing and weepy eyes. This lifelong, relapsing pattern is why an apparently healthy cat may have flare-ups for years.
The eye complications deserve particular respect. Severe or repeated infection can scar the surface of the eye or cause corneal ulcers, and in kittens overwhelming infection occasionally damages the eyes permanently. Any cat holding an eye shut, or with a cloudy or ulcerated cornea, should be seen promptly. Most flare-ups, though, are milder — a few days of sneezing and runny eyes that settle with gentle nursing and good food.
Vaccination is the foundation of control. The core kitten vaccine includes FHV-1 and, boosted through life, takes much of the sting out of the disease even though it cannot guarantee a cat will never be infected. Because stress reactivates the virus, the other half of management is simply keeping life calm and predictable for cats prone to flare-ups, and acting early when the tell-tale sneezing and weepy eyes return.
🔍 Causes
Feline herpesvirus type 1 (FHV-1) spreads through eye, nose and mouth secretions — by direct contact, shared bowls or bedding, sneeze droplets, and on human hands. Once a cat is infected it carries the virus for life, lying dormant in the nerves and reactivating at times of stress (rehoming, a new pet, boarding, or other illness), which is why a cat that seemed fully recovered can flare up again months or years later.
🛡 Prevention
FHV-1 is covered by the core "flu and enteritis" vaccine given to every kitten and boosted through life — it does not always prevent infection but dramatically reduces how severe and how frequent flare-ups are. Minimising stress, keeping vaccinations current, isolating sneezing cats, and good hygiene in multi-cat homes and shelters all help limit spread and reactivation.
💊 Treatment
As with calicivirus, no drug eliminates the virus, so care is supportive: keeping the nose and eyes gently cleaned, tempting the cat to eat with warm, aromatic food, and maintaining hydration. The amino acid L-lysine is sometimes used to reduce the severity of flare-ups. Eye involvement may need topical antiviral or lubricating drops, and secondary bacterial infections are treated with antibiotics. Severe corneal ulcers occasionally require referral to a veterinary ophthalmologist.
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⚕️ Medical disclaimer
- This information is educational only and is not a substitute for veterinary advice.
- Symptoms overlap between conditions — only a vet can diagnose accurately.
- Never withhold treatment or self-medicate based on information found online.
- When in doubt, call your vet. Early intervention almost always leads to better outcomes.